STAT proteins were originally discovered as latent cytoplasmic transcription factors that mediate cytokine and growth factor responses (Darnell, J. E., Jr. (1996) Recent Prog. Norm. Res. 51, 391-403; Darnell. J. E. (2005) Nat. Med. 11, 595-596). Seven members of the family, STAT1, STAT2, STAT3, STAT4, STAT5a and STAT5b, and STAT6, mediate several physiological effects including growth and differentiation, survival, development and inflammation. STATs are SH2 domain-containing proteins. Upon ligand binding to cytokine or growth factor receptors. STATs become phosphorylated on critical Tyr residue (Tyr705 for STAT3) by growth factor receptors, cytoplasmic Janus kinases (Jaks) or Src family kinases. Two phosphorylated and activated STAT monomers dimerize through reciprocal pTyr-SH2 domain interactions, translocate to the nucleus, and bind to specific DNA-response elements of target genes, thereby inducing gene transcription (Darnell, J. E., Jr. (1996) Recent Prog. Norm. Res. 51, 391-403; Darnell. J. E. (2005) Nat. Med. 11, 595-596). In contrast to normal STAT signaling, many human solid and hematological tumors harbor aberrant STAT3 activity (Turkson, J. Expert Opin. Ther. Targets 2004, 8, 409-422; Darnell, J. E., Jr. (1996) Recent Prog. Norm. Res. 51, 391-403; Darnell. J. E. (2005) Nat. Med. 11, 595-596). In contrast to normal STAT signaling, many human solid and hematological tumors harbor aberrant STAT3 activity (3 and Darnell. J. E. (2005) Nat. Med. 11, 595-596; Bowman, T., et al. (2000) Oncogene 19, 2474-2488; Buettner, et al. (2002) Clin. Cancer Res. 8, 945-954; Yu, H. and Jove. R. (2004) Nat. Rev. Cancer 4, 97-105; Haura, E. B., et al. (2005) Nat. Clin. Pract. Oncol. 2, 315-324).).
Constitutive STAT3 activity mediates dysregulated growth and survival, angiogenesis, as well as suppresses the host's immune surveillance of the tumor, making constitutively-active STAT3 a critical molecular mediator of carcinogenesis and tumor progression.
Genetic and other molecular evidence reveals persistent Tyr phosphorylation of STAT3 is mediated by aberrant upstream Tyr kinases and shows cancer cell requirement for constitutively-active and dimerized STAT3 for tumor maintenance and progression. Thus, in numerous proof-of-concept studies (Turkson, J.; et al. Mol. Cancer Ther. 2004, 3, 261-269; Turkson, J.; et al. J. Biol. Chem. 2001, 276, 45443-45455; Siddiquee, K.; et al. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 7391-7396; Turkson, J.; et al. Mol. Cancer Ther. 2004, 3, 1533-1542; and Turkson, J.; et al. J. Biol. Chem. 2005, 280, 32979-32988),
inhibition of STAT3 activation or disruption of dimerization induces cancer cell death and tumor regression. How aberrant STAT3 is regulated for meeting the tumor-specific requirements in malignant cells remains undefined. There have been no studies into defining the molecular details of how malignant cells regulate aberrant STAT3 and how this regulation changes upon STAT3 inhibition prior to the onset of phenotypic changes, although knowing these events will facilitate efforts in modulating aberrant STAT3 for managing human cancers. Small-molecule STAT3 inhibitors thus provide tools for probing the molecular dynamics of the cellular processing of STAT3 to understand STAT3's role as a signaling intermediate and a molecular mediator of the events leading to carcinogenesis and malignant progression.
Stat5 signaling, like Stat3 signaling, is transiently activated in normal cells and is deactivated by a number of different cytosolic and nuclear regulators, including phosphatases, SOCS, PIAS, and proteasomal degradation. Like Stat3, Stat5 has gained notoriety for its aberrant role in human cancers and tumorigenesis, having been found to be constitutively activated in many cancers, including those of the breast, liver, prostate, blood, skin, head and neck. (Müller, J., et al. ChemBioChem 2008, 9, 723-727). In cancer cells, Stat5 is routinely constitutively phosphorylated which leads to the aberrant expression of Stat5 target genes resulting in malignant transformation. Cancer cells harbouring persistently activated Stat5 over express anti-apoptotic proteins, such as Bcl-xL, Myc and MCL-1, conferring significant resistance to natural apoptotic cues and administered chemotherapeutic agents. Of particular interest, Stat5 has been identified as a key regulator in the development and progression of acute myelogenic (AML) and acute lymphoblastic leukemias (ALL; Gouilleux-Gruart, V., et al. Leukemia and Lymphoma 1997, 28, 83-88; Gouilleux-Gruart, V., et al. Blood 1996, 87, 1692-1697; Weber-Nordt, R. M., et al. Blood 1996, 88, 809-816). Moreover, inhibitors of upstream Stat5 activators (such as JAK and FLT3) have been shown to exhibit promising anti-cancer properties (Pardanani, A., et al. Leukemia 2011, 25, 218-225; Quintás-Cardama, A., et al. Nature Reviews Drug Discovery 2011, 10, 127-140).
Despite advances in drug discovery directed to identifying inhibitors of STAT protein activity, there is still a scarcity of compounds that are both potent, efficacious, and selective activators of STAT3 and STAT5 and also effective in the treatment of cancer and other diseases associated with dysfunction in STAT3, STAT5 or both proteins, and diseases in which one or both of STAT3 and STAT5 is involved. These needs and other needs are satisfied by the present invention.